I found this information at http://www.netwelding.com/ignition_timing.htm regarding the recommended timing curve for a ZZ502.RPM Degrees BTDC

800 10

1050 10

1250 12

2030 25

3000 28

4170 30

4630 31


My question is whether or not anyone feels that this accurate for my combination.

I am currently running a ZZ502 with an Edelbrock Air Gap intake and a Holley 850 (mechanical secondaries).

Right now, the motor has a cough at about 1800-2000 that I would like to get rid of. After that, it takes off like a rocket ship!

I've set the initial at 8° BDTC and verified that it has 34° at about 4,000 RPM.

Here is the distributor that I am using http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2D850050&N=700+400304+115&autoview=sku

It has the lightest springs on the weights that came in the kit with the distributor.

I haven't checked to see if it is advancing to 25° at 2030 RPM yet, but, I will if everyone thinks that this is an accurate curve.

BTW, any comments on replacing the distributor gear? Should I use the GM # 10456413 gear? The valve train is the stock ZZ502 setup.

Timing is optimized for the application. How you drive, vehicle weight and gearing, cam and compression enter into it as well. My suggestion is to find a performance oriented mechanic I would talk to roundy-rounders as they seem to live and dream about accelerating from a corner which will most likely emulate driving on the street (compared to a pro stock 500 cube BBC that launches at 7,800 RPM and shifts at 10,000). You have to consider your driving style and have realistic expectations to work with the guy who will set up the advance curve and check it in his shop.

Larger Dave

Timing is optimized for the application. How you drive, vehicle weight and gearing, cam and compression enter into it as well. My suggestion is to find a performance oriented mechanic I would talk to roundy-rounders as they seem to live and dream about accelerating from a corner which will most likely emulate driving on the street (compared to a pro stock 500 cube BBC that launches at 7,800 RPM and shifts at 10,000). You have to consider your driving style and have realistic expectations to work with the guy who will set up the advance curve and check it in his shop.

Larger Dave

Dave is right on about application being the key to timing. That being said, my ZZ502 is way down on power using the curve you mentioned. I use 18 degrees initial and 37 degrees at 3000 RPM and it woke the 502 up! I went with the MSD Digital E- Curve # 8394 as it is so easily programed. At the afore mentioned 8 degree timing, my engine would pop back or just be lazy on acceleration. Correct timing is the key to the engines horsepower.

Back in the old days;) ,,,,,
Seriously, BBC's like timing. What are you driving, a grocery getter or a hotrod engine? You were told good scoop. I've run 12* initial, 42* total, all in at 2600, since 1970. Works great. Yes, octane booster is a good thing.:thumbsup:

GM calls for 36* total timing. Rev the motor up till it stop advancing, and move the dizzy till you get 36* - thats it. You will have to live with the initial, whuich seems awfully low. That thing has a 26* mechanical curve? That sucks. I suggest 18-20* curve so you can run 16-18 initial and the 36* total. That 502 will want more initial than 8-10*.

Thanks for all the replies. I'm gonna try to just bump up the initial timing to see how it responds.

Anyone have any comments on the distributor gear?

Is the GM gear (10456413) an absolute must have?

Thanks for all the replies. I'm gonna try to just bump up the initial timing to see how it responds.

Anyone have any comments on the distributor gear?

Is the GM gear (10456413) an absolute must have?

Yes...get the "melonized" gear on there yesterday. You WILL tear the gears up if you dont use the right one.

I bought a ZZ502 take out distributor off of esbay for 75.00. Has the gear on there already, and a pretty fast curve. Only thing I dont like is that it has a 22* curve, which means I have to run 14* initial for the 36* total. I modified it so now I run 22* initial 36* total.

I needed this post.
I'm running my ZZ502 at 10* initial....never checked the total. It's a stock Pertronix disti. I haven't even changed the advance springs yet.
The engine runs real strong, but in the upper RPM it makes a popping sound that I thought was valve float related....could it be timing related?

Tim

I changed the distributor gear (GM # 10456413) today. Now I can sleep at night...

As far as the timing, I was a little worried that the distributor wasn't getting up to the 25° advance at 2030 RPM (in my earlier post). Turns out it was about dead on (around 24°).

I also changed to the red busing in the advance weight and set the timing to get 10° initial. Ended up with about 39° total advance.

The busing diameter that I had in there (going off memory) was around .350" diameter O.D. The one that I put in (the red one) was about .320" OD.

What does the red bushing do? I believe that it gives me more advance. Is that correct?

I also found out that my 850 Holley had #72 jets (primary and secondary). Changed those to #78 primary and #80 Secondaries.

All I can say is that it is now, by far, the sweetest running motor I have ever owned.

I just can't get rid of that grin!!!:D

So, I do have a Holley Commander MPFI and a procharger. Should I?;)

Thanks to everyone for the input. I couldn't imagine building a car without everyones input!

Truth in advertising is all I have to say about the ZZ502. Best big block GM ever sold, and I went through three L-88s and an LS-7 back in the early seventies (though the LS-7 was a sweet motor).